This thesis focuses on the study of transient and variable radio sources in the universe. Transient signals, unlike a source constantly visible, change in their brightness (or flux) over a certain... Show moreThis thesis focuses on the study of transient and variable radio sources in the universe. Transient signals, unlike a source constantly visible, change in their brightness (or flux) over a certain length of time. While there are a plethora of transients over short intervals in radio astronomy that last less than a minute, this thesis will primarily cover those which play out over many years and decades. Show less
Whereas the extreme conditions of the first minutes after the Big Bang have produced nearly all the hydrogen and helium in the Universe, heavier elements - or metals - are synthesised in the... Show moreWhereas the extreme conditions of the first minutes after the Big Bang have produced nearly all the hydrogen and helium in the Universe, heavier elements - or metals - are synthesised in the core of stars and in supernova explosions. Currently, however, the behaviour of supernovae (and their stellar progenitors) is not well understood, and could be better constrained by measuring accurately the relative amount of metals they produce. On the other hand, the very hot and diffuse gas - or intra-cluster medium (ICM), glowing in X-ray and detected in the large gravitational potential well of galaxy clusters and groups, is also rich in metals. This means that the building blocks of life, synthesised by billions of supernovae over cosmic times, are present even at the largest scales of the Universe, as they enrich the ICM. In this thesis, I show how measuring the abundances of O, Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni in a sample of nearby, relaxed galaxy clusters, groups, and ellipticals observed with XMM-Newton (the CHEmical Enrichment Rgs Sample) helps to better understand Type Ia and core-collapse supernovae, as well as the history and conditions of the ICM enrichment in general. Show less
This thesis uses catastrophic stellar events (supernovae and stellar collisions) to investigate different aspects of their environment. The first part of the thesis examines what happens to... Show moreThis thesis uses catastrophic stellar events (supernovae and stellar collisions) to investigate different aspects of their environment. The first part of the thesis examines what happens to supernova remnants near supermassive black holes like the one in the Milky Way Galaxy. To do so, a technique is first developed for predicting the evolution of supernova remnants in non-uniform densities. This is used to demonstrate how supermassive black hole environments determine the evolution and lifetime of supernova remnants. Conversely, observations of supernova remnants can then be used to infer properties of the surroundings of supermassive black holes. Therefore, predictions are then given for the X-ray emission that could be observed from core-collapse supernova remnants in these regions. This emission can compete with other sources, such the accretion flow of the supermassive black hole itself. Next, the problem of a core-collapse supernova in a close binary system is considered, where the effect on the companion is studied to predict the properties of runaway stars from binaries disrupted after a supernova. Finally, simulations of blue stragglers, formed from stellar collisions, are used to learn about the globular clusters containing them. Estimating the collision times reveals details about the evolutionary history of the cluster. Show less
